A photoconductive process using an electrophotographic light-sensitive material includes a first step of generating electric charges by exposure and a second step of transporting the electric charges.
These steps can be conducted in a single substance such as selenium light-sensitive plate. Alternatively, the two steps can be performed in different substances such as by using a combination of amorphous selenium and poly-N-vinylcarbazole for the first and second step, respectively. The process in which the steps are conducted in different substances has the advantage that the substances used for electrophotographic light-sensitive materials can be selected from an expanded group and, consequently, electrophotographic characteristics such as sensitivity or accepting electric potential of the electrophotographic light-sensitive materials can be improved. Substances suitable for producing the coated film in the electrophotographic light-sensitive materials can also be selected from a wide variety of such substances.
Conventional photoconductive substances for electrophotographic light-sensitive materials used in electrophotography have included inorganic substances such as selenium, cadmium or zinc oxide.
Electrophotography, as disclosed in U.S. Pat. No. 2,297,691 to Carlson, uses a photoconductive material comprising a base coated with a substance which is insulating in the dark, and having an electric resistance which changes according to the amount of exposure received during imagewise exposure. After this photoconductive material is kept in the dark for a suitable period, the surface is uniformly charged in the dark. Then, this material is imagewise exposed to light using an irradiation pattern having the effect of reducing the surface electric charge in a pattern corresponding to the relative energy contained in various parts of the irradiation pattern. The surface electric charge or electrostatic latent image left on the surface of the photoconductive substance layer (electrophotographic light-sensitive layer) is then contacted with a suitable electroscopic indicating substance, e.g., toner, to form a visible image.
The toner is contained in an insulating liquid or a dried carrier, and in either case it adheres to the surface of the electrophotographic light-sensitive layer according to the electric charge pattern. The adhering indicating substance can be fixed by known means such as by heat, pressure or vapor of a solvent. The electrostatic latent image can be transferred to a second support (for example, paper or films). The electrostatic latent image can be developed on the second support in a similar fashion after being transferred. Electrophotography is one image forming process in which the image is formed as described above.
In such an electrophotographic process, the basic characteristics required for electrophotographic light-sensitive materials are that (1) they can be electrified in the dark so as to have a suitable electric potential, (2) the disappearance of electric charge in the dark is small, and (3) the electric charge can be rapidly reduced by exposure to light.
The above described inorganic substances conventionally used in electrophotographic processes have both faults and advantages. For example, selenium which is widely used at present satisfies the above described requirements (1) to (3), but has the disadvantages that its production requires severe conditions and high production cost, it is inflexible and difficult to process into a belt-like form, and it requires careful handling because it is sensitive to heat and mechanical impact. Cadmium sulfide and zinc oxide are used as electrophotographic light-sensitive materials dispersed in a resin which is a binder. However, they cannot be repeatedly used in such a state, because of mechanical deficiencies in smoothness, hardness, tensile strength and friction resistance.
In recent years, to improve these faults of inorganic substances, electrophotographic light-sensitive materials using various organic substances have been proposed and some of them have been put in practical use. Examples include electrophotographic light-sensitive materials containing poly-N-vinylcarbazole and 2,4,7-trinitrofluoren-9-one. (U.S. Pat. No. 3,484,237), or poly-N-vinylcarbazole sensitized with pyrylium salt type dyes [Japanese Patent Publication No. 25658/73 (U.S. Pat. No. 3,617,268)], electrophotographic light-sensitive materials containing an organic pigment as a main component [Japanese Patent Application (OPI) No. 37543/72 (U.S. Pat. No. 3,898,084)] and electrophotographic light-sensitive materials containing an eutectic crystal complex composed of a dye and a resin as a main component [Japanese Patent Application (OPI) NO. 10785/72 (U.S. Pat. Nos. 3,732,180 and 3,684,502)] (the term "OPI" as used herein refers to a "published unexamined Japanese patent application").
In these organic electrophotographic light-sensitive materials, although the disadvantageous mechanical characteristics and flexibility described in inorganic electrophotographic light-sensitive materials are improved to some degree, their light sensitivity is low and they are not suitable for repeated use, and are consequently insufficient for practical use in electrophotographic light-sensitive materials.